Bileaflet heart valve having open channel and swivel pivots

ABSTRACT

A bileaflet heart valve comprising an annular base and pivoting leaflets. Each leaflet is “free-floating” within recesses without fixed rotational axis in order to increase translational movement and redistribute stresses. Each recess fluidly communicates with a groove extending at least partially around the inner surface of the annular base and fluid flow is directed through the recesses at different angles during antegrade circulation, retrograde circulation, and valve closure. A recess entrance angle to each of the recesses preferably being less than about 35° and the pivoting mechanism within the recess including first and second fulcrum edges of each leaflet shiftably engaged with side surfaces of the respective recesses. The leaflets have a beveled bottom side having two separate planar surfaces which lie at an angle to one another. In preferred embodiments, an upper planar surface of the bottom surface of each leaflet lies at an angle of greater than ninety (90) degrees with respect to a horizontal passing through a section of the annular base when the leaflet is in a fully open position.

CO-PENDING APPLICATIONS

The present application claims priority to U.S. Provisional applicationSer. No. 60/060,922, filed Oct. 3, 1997, and relates to U.S. patentapplication Ser. No. 09/143669, filed Aug. 31, 1998, now abandoned whichis a continuation of U.S. patent application Ser. No. 08/626,170, filedMar. 29, 1996, now U.S. Pat. No. 5,824,062, which is acontinuation-in-part of both U.S. patent application Ser. No. 08/412,696filed Mar. 29, 1995, now abandoned, and U.S. patent application Ser. No.08/546,210 filed Oct. 20, 1995, now abandoned, each of which is entitledBILEAFLET HEART VALVE.

FIELD OF THE INVENTION

The present invention relates generally to bileaflet hemodynamic heartvalve prostheses of the type permitting translational and rotationalmovement of the leaflets, and particularly to a low-excursion prostheticheart valve suitable for mitral valve replacement involving preservationof the papillary muscle and chordal structure wherein the valve may beoriented in either an anatomical or anti-anatomical configuration.

BACKGROUND OF THE INVENTION

The replacement of defective heart valves with hemodynamic prostheses isthe most prevalent course of treatment for certain types of heartdisease and dysfunction affecting the atrioventricular valves—namely theright AV (tricuspid) and the left AV (bicuspid) valves. Although avariety of tissue and prosthetic heart valve mechanisms have beendeveloped, monoleaflet (tilting disc) and bileaflet valves currentlyhold the greatest measure of acceptance among practitioners. Thesevalves include one or two pivoting leaflets or occluders retained withina seating collar or suture ring that is implanted in place of thephysiological valve.

Replacement of a bicuspid (mitral) valve using a procedure thatpreserves portions of the papillary muscle and chordal apparatus isdiscussed herein for exemplary purposes. In that procedure, the anteriorleaflet is bisected and detached from the annulus, and the two halvesare groomed and then sutured to the posterior mitral annulus with thepapillary muscle and chordal apparatus substantially intact. Such aprocedure and its benefits are described in significant detail by H.Feikes, et al., Preservation of All Chordae Tendineae and PapillaryMuscle During Mitral Valve Replacement with a Titling Disc Valve, 5 J.Cardiac Surg., No. 2 pp. 81-85 (1990). The authors conclude that thismitral valve replacement procedure can be practical using bothmonoleaflet and bileaflet valves. However, it is readily apparent tothose skilled in reconstructive cardiac surgery that selection of asuitable valve type and proper orientation of the prosthesis can beimportant factors impacting the long term success of this procedure fora given patient. In particular, due to the position at which the valvetissue is sutured to the posterior mitral annulus, care must be taken toensure that the peripheral edge of a leaflet does not contact the tissueduring normal operation of the valve. Such contact can result in theintermittent, partial, or complete malfunction of the valve, as well asdamage to or dislodgement of the valve tissue.

Four primary combinations of valve types and orientation are considered,as diagramed in FIGS. 25-28 herein. The four combinations ranked byascending level of risk include: (1) monoleaflet valve M with anteriororientation (FIG. 25); (2) bileaflet valve with anti-anatomicalorientation (FIG. 26); (3) bileaflet valve with anatomical orientation(FIG. 27); and (4) monoleaflet valve M with posterior orientation (FIG.28). While the monoleaflet with posterior orientation is generallyregarded as a high risk configuration and the monoleaflet with anteriororientation is considered to have little or no risk, the degree of riskassociated with a bileaflet valve oriented in either the anatomical oranti-anatomical configuration depends upon the particular type of valveselected (particularly its range of excursions, radial exposure, andlateral exposure), the post-procedure anatomical characteristics of theannuls, and the patient's requirement for certain operational parametersassociate with the valve.

While a monoleaflet valve may be preferred in order to achieve thelowest risk level with an anterior orientation, a physician may preferto implant a bileaflet valve to obtain specific functional benefitsassociated with or unique to the particular bileaflet valve structure.

The bileaflet valve has been extensively developed and refined. However,there is still room for further improvement. Problems associated withthe weakening or structural failure of critical components in the valveare linked both to dynamic mechanical stresses and cavitation. It isnoted that a certain amount of antegrade and retrograde leakage isgenerally anticipated. However, the amount of leakage is preferablymaintained within acceptable limits corresponding roughly to normalanatomical valves. In addition, minimizing the physical size of thevalve prosthesis, particularly the longitudinal dimensions of theannular base, produces greater excursion along the peripheral edges ofthe leaflets, while simultaneously increasing the difficulty in raisingthe heights of the pivot axis. Furthermore, recesses, crevices, corners,and obstructions required to restrain the leaflets within the annularbase and maintain pivotal movement also interfere with circulation,create turbulence, and produce zones of stagnation, each potentiallyproviding a thrombogenic nidus that may eventually lead to an embolism.Although bileaflet valves are hemodynamic, spacing the fixed axis ofrotation of the leaflets significantly apart from the secondary naturalaxis of rotation limits the maximum speed or angular rate which theleaflets may attain during opening and closing.

In regard to the selection of suitable materials, there is an inherentbalancing between the selection of materials for ease of fabrication,biocompatibility, strength, and weight versus selection with respect tothe acceptable level of fragility of the resulting components,particularly those involving delicate structures such as wire guides,cages, and pins that bear significant loads. In addition, the structureof many pivot mechanisms requires the annular bases to have opposingflat sides rather than a substantially or completely circular bore,thereby restricting the maximum flow volume and increasing the valve'snominal fluid pressure.

U.S. Pat. No. 4,276,658 to Hanson provides a representative example of aconventional bileaflet heart valve. That valve utilizes a pair ofsemicircular pivot “ears” disposes on opposing sides of each leafletreceived within “hourglass-shaped” slots to control the pivotal movementof the leaflets—including the angular sweep between the open and closedpositions, the tiling of the valve away from its restrained pivotalaxis, and the translational movement of the leaflet both parallel withits normal plane and along the linear flow path through the bore of theannular base. The Hanson '658 patent also describes the use of apyrolytic carbon coating over a metallic or synthetic substrate forfabrication of the valve's components.

For comparison, U.S. Pat. Nos. 4,240,161 to Huffstutler and 3,859,668 toAnderson provide representative examples of the features, structure, andoperation of monoleaflet or “titling disc” heart valves.

Various improvements directed toward correcting the deficienciesdescribed above have been developed, each achieving varying degrees ofsuccess and accompanied by inherent tradeoffs with other beneficialfeatures.

U.S. Pat. No. 3,903,548 to Nakib discloses an effort to utilize thebeneficial features of the monoleaflet principle in a bileaflet valvethat similarly omits fixed pivotal axis, however the resulting cagestructure produces an unacceptably small effective bore andcorrespondingly high pressure gradient across the valve.

In a bileaflet valve structure such as disclosed in the Hanson '658patent, the leaflets may each pivot filly between the open and closedportions on the order of 80,000-120,000 times per day given a standardpulse of 60-80 beats per minute. Movement of the leaflets through aviscous aerated fluid such as blood may produce significant cavitation—the formation of partial vacuums caused by sudden movement of theflowing fluid away from the surface of the leaflets as a result ofmechanical forces exerted by the leaflets. These partial vacuums produce“micro bubbles” on or near the surface of the leaflets, and when thepressure is released, vacuums change into positive pressure regionswhich lead to implosion of bubbles which can cause pitting of thesurface of the leaflet. The cavitation potential is amplified greatly bythe virtually instantaneous stopping and starting of the leaflets asthey contact a rim along the annular base and also, in the casestopping, by the rate of speed at which the leaflet is traveling when itstops. Contact between the leaflet and the rim greatly increases thecompressive forces on the adjacent fluid, and as the leaflet pivots awayfrom the rim the corresponding effects of the expansions are magnifiedby increased negative pressures and stronger partial vacuums. Whereasstandard cavitation produces pitting of metal surfaces due only tomechanical contact between the flowing fluid and moving object,introducing reciprocal movement and mechanical contact within the fluidcause the collapsing cavitation bubbles to strip or shear material fromthe leaflet surfaces at an accelerated rate. Although the surfacepitting occurs at a near microscopic level, the result is surfacedegradation of the leaflet which can induce stress fractures andfragmentation leading to the premature failure of a leaflet.

U.S. Pat. No. 4,078,268 to Possis discloses a substantially circularbore through the annular base, as well as a nearly complete separationbetween the peripheral edges of the leaflets and the annular base aroundthe circumference of the valve. While this design obviates certaincavitation problems, it permits high levels of antegrade and retrogradeleakage and places the entire load of restraining each leaflet on a pairof pivot pins received within adjustable bearing plugs. The combinationof increased torque, absorbed impact forces, vibration, and normalfrictional contact are believed to exert undue mechanical stresses onthe relatively delicate pivot pins and bearing plugs.

U.S. Pat. No. 5,080,669 to Tascon discloses an annular base that defineschannels which intersect the pivot axis of the leaflets at variousangles to direct flow of blood around enlargements in the leaflets thatserve as the pivot axis, in an effort to cleanse the surfaces of theenlargements and prevent zones of thrombogenic stagnation from forming.However, the inward projections forming the channels and barriersrestraining the leaflets in the Tascon '669 design create obstacles touniform blood flow through the bore of the annular base, and defineacute corners and crevices which can accelerate the formation of athrombus. In addition, the enlargements continuously block a majority ofthe potential flow through each of the channels, thereby minimizing anycleansing effect that is realized.

U.S. Pat. No. 4,892,540 to Vallana discloses a pair of vertical“chimneys” defined by the lobes of the annular base and communicatingwith the recesses in which the ears of the respective leaflets arereceived. In concept, blood flow in either the antegrade or retrogradedirection passes between the pivot ears and the side wall of the annularbase to cleanse the recess. However, the angled base portions formingeach wedge-shaped separator body hold the pivot ears and leaflets in anelevated position proximate to the inlet from the chimney into therecess, thereby minimizing flow through the chimney. The pivot earseither reduce the flow rate within the recess or divert the flow awayfrom portions of the recess where stagnation could occur, thusdiminishing the effectiveness of any cleansing action. Whereas Tascon'669 contemplates alternating between multiple flow paths oriented atdiverse angles to enhance the “scrubbing” effect, Vallana '540 onlycontemplates cleansing that is substantially repetitive and reciprocalalong one path for both antegrade and retrograde flow. Finally, to theextent that Vallana '540 would produce an acceptable retrogradecleansing action due to the pressure differential created within therecess feeding into the chimney, it is at the expense of a significantlyrestricted non-circular bore through the annular base accounting for asubstantial reduction in antegrade circulation.

Although the Hanson '658 patent discloses the pivot ears preventingblood stagnation in the area of engagement with the recesses, the use oftransesophageal echocardiography in patients receiving mitral valvereplacements has shown the formation of dangling fibrin strands alongthe interior surface of the valve in the areas between and proximate tothe pivot recesses. These small filamentous abnormal echoes (SAE) areconsidered non-obstructive while within the valve, however theirfrequent disappearance strongly suggests a thrombotic origin and asignificant correlation with the risk of early thrombogenic episode hasbeen observed.

Many factors may be responsible for the formation of the fibrin strands,including regions of blood stagnation which provide a nidus forthrombogenic formations, or defects in the materials or structure of thevalve that permit the direct attachment of blood cells. It may thereforereadily be appreciated that two important goals when designing abileaflet heart valve are maintaining optimal antegrade and retrogradecirculation, and eliminating regions of reduced circulation within thevalve that might foster the development of a thrombogenic mass. It issuggested that while the Hanson '658 patent shows a relatively shallowsemi-circular recess, in practice it has not been possible to achieve aworkable commercial embodiment of a bileaflet valve having pivot earswith a suitably shallow recess to enhance cleansing of the recess bynormal antegrade and retrograde circulation. For example, thecommercially available embodiments of the Hanson '658 valve haverecesses forming entrance angles ranging from 35° to 48° measuredbetween the lateral wall of the bore and the tangentially adjoiningsurface of the recess, depending upon overall size of the valve.Recesses forming an angle of 35° or less with the adjoining lateral wallhave been achieved in monoleaflet valves, however the significantlydifferent structure and operation of monoleaflet valves has notpermitted the successful utilization of many comparable features inbileaflet valves.

Various adaptations have also been made in an effort to improve thepivot mechanism. One option is to eliminate the pivot ears or pins, andallow the leaflet to rock on projections extending inwardly from theannular base. These configurations generally require some engagementbetween the leaflet and the projections—either the projection beingreceived within a notch or recess in the leaflet, or the leaflet forminga trapping flange that prevents egress from between two spaced-apartprojections. For example, U.S. Pat. Nos. 4,863,459 to Olin and 4,935,030to Alonso describe leaflets that include a swelled area or cammingsurface trapped between two projections. U.S. Pat. Nos. 4,373,216 toKlawitter, 4,692,165 to Bokros, 4,872,875 to Hwang, and 5,354,330 toHanson each describe a variation in which the leaflet defines aperipheral notch or recess receiving a projection the annular base.While designs utilizing a notch in the leaflet are more secure than thetrapped flange configurations, they are also more difficult to assemblewithout placing undue stress on the leaflets or projections. Inaddition, these designs similarly present flat-sided bores andprojections which extend into the bore and obstruct antegrade flow. Asthe complexity of these projections increases, the opportunity for acrevice or recess providing a thrombogenic nidus also increases.Representative examples of relatively complex pivot structures thatpresent several potential stagnation sites include U.S. Pat. Nos.5,116,367 to Hwang and 5,123,920 to Bokros.

One prominent feature of the bileaflet valves discussed above is thedegree of exposure or incursion that is exhibited by the leafletsrelative to the annular base. Excursion can be thought of as the maximumdistance which the distal ends of the leaflets protrude from the bottomof the annular base when the valve is completely open, measured from thelowermost planar surface of the base to the most distal point on theperipheral edge of the respective leaflet. However, when comparing theanatomical and anti-anatomical orientation of a bileaflet valve withreference to the mitral valve replacement procure discussed above,incursion can also encompass two more complex relationships.

U.S. Pat. Nos. 5,246,453 to Bokros and 5,002,567 to Bona disclosealternate configurations in which the leaflets are not generally planar,and are supported by and pivot about fulcrums disposed on the lowerportion of each leaflet. While these designs present an incursion bothabove and below the annular base, it allows the height of the annularbase to be reduced somewhat relative to comparable bileaflet valves.While such a design is considered to be more responsive to reversal inthe antegrade flow, it also relies upon shifting the axis of rotationrelative to the leaflet's moment of inertia and therefore producesdifferent operational characteristics than might normally be expected.

One factor previously alluded to which affects the speed at which thevalve operates, is the displacement between the fixed axis of rotationand the corresponding En moment of inertia of the leaflet. Anotherfactor is the shape of the leaflet. In this regard, optimization ofseveral physical parameters must be contemplated. The leaflets must movethrough an arcuate path in response to fluid pressure applied from boththe antegrade and retrograde directions, starting from differentialinitial orientations relative to the fluid pressure, and within aninitially static versus initially dynamic environment. Consequently,valves having superior opening characteristics may be slow to close orresist complete closure, and vice versa. Leaflets having an angled,curved, or bicurved design to enhance the immediate responsiveness tochanges in hemodynamic forces can be employed to address this problem.Other factors include reducing turbulence or backwash that might resistthe leaflet's momentum or increase its apparent resting inertia,reducing the weight or thickness of the leaflet, allowing the leaflet torock or cam differently in response to antegrade or retrogradepressures, maximizing the laminar flow through the valve body over theentire leaflet surface, and eliminating sources of friction, vibration,or misalignment that could adversely affect the mechanical operation ofthe valve.

Another approach mentioned above is to increase the translationalmovement of the leaflet within the annular body, thereby permitting theleaflet to pivot more naturally about its inertial axis in directresponse to the hemodynamic forces. This approach can potentially bemore beneficial than merely moving the fixed axis of rotation nearer tothe moment of inertia, since it also serves to reduce frictional forcesand other physical impediments to proper valve operation. One limitationis the need to maintain proper alignment and seating of the leafletwithout encumbering the flow passage with obstructions or incorporatingfree structures that increase the likelihood of valve failure.

U.S. Pat. No. 4,535,484 to Marconi describes a bileaflet valve in whichthe leaflets are “free-floating”, thereby increasing translationalmovement and reducing the mechanical stresses imposed at localized pivotpoints and other load bearing surfaces. However, the Marconi '484 designrequires a complex and fragile cage structure to restrain the leaflets,thereby producing a significant risk of damage to the valve duringmanufacturing or handling and increasing the potential for catastrophicfailure of a valve component that would result in death or severe injuryto the patient, mitigating against the use of certain materials such aspyrolytic carbon, and greatly increasing the cost and complexity offabrication.

For comparison, U.S. Pat. No. 4,689,046 to Bokros describes atrapezoidal pivot ear having beveled edges, arguably decreasing thetranslational freedom, but enhancing the “sweeping” effect of the pivotear to prevent thrombogenic formations within the recesses anddistributing lateral stresses over a wider surface area.

It will also be appreciated from analyzing bileaflet heart valves, suchas disclosed by the Hanson '658 and Possis '268 patents, that theleaflets divide the bore into three passages having unequalcross-sectional areas, and that corresponding effects on fluid dynamicsshould be expected. Observation of these valves in operation shows thatflow rates through the passages will vary generally inversely with thecorresponding cross-sectional area. As such, in a valve such as Hanson'658 which present a relatively narrow central passage, the flow rate ofblood passing through that central passage is greater than through thetwo passages on opposing sides. The faster blood flow in the center,relative to the sides, can cause additional turbulence within ordownstream of the valve, or produce a pressure differential or venturieffect within the valve that can impede or retard the optimaltranslational or pivotal movement of the leaflets. The Possis '268 valvepresents a larger central passage with narrower cross-sectional passageson each side, thereby reversing the fluid dynamics compared with theHanson '658 design.

While many common functional goals have been recognized among designersof bileaflet heart valve prostheses, there are strongly divergentopinions concerning the prioritization of those goals and how best toachieve specific results or advantages. Accordingly it will be readilyappreciated that these competing factors significantly influence thedesign and optimization of all bileaflet heart valves and that furtherimprovements may be made. The present invention provides advantages overthe prior art bileaflet heart valves and solves problems associatedtherewith.

SUMMARY OF THE INVENTION

Briefly described, the bileaflet heart valve prosthesis of the presentinvention comprises an annular base defining a substantially circularbore, and a pair of pivoting leaflets; each of the respective leafletshaving first and second sides, the first side being a top side and thesecond side being a bottom side, the bottom sides of the respectiveleaflets generally facing one another when the respective leaflets arein an open position; each bottom side having an upper half and a lowerhalf, a major portion of the upper half providing an upper surface lyinggenerally in a first plane and a lower half providing a lower surfacelying generally in a second plane, the first plane lying at an angle tothe second plane; a third plane passing through a horizontalcross-section of the annular base, the first and second planes lying atangles to the third plane when the leaflets are in either the open orclosed positions; wherein the first plane of each of the respectiveleaflets extends beyond an angle of 90° with respect to the third planewhen the leaflets go from the fully closed position to the fully openposition.

The first plane can extend beyond a 90° angle with respect to the thirdplane when the leaflets go from the fully closed position to the fullyopen position without diminishing the leverage for closure of theleaflets when the leaflets are in the fully open position. This isbecause the lower portion of the bottom side of the leaflets remain at asuitable angle to allow for adequate leverage against the lower portionof the leaflet, to shift the leaflets within the respective recesses andpivot the leaflets to the closed position once the upper fulcrum edgecomes into contact with the upper sidewall of the respective recess.

In preferred embodiments the leaflets have a beveled bottom side whichminimizes the travel angle “k′” between the open and closed positions.The lateral ends of each leaflet are received within “open channel”recesses where the ends are “free floating”, permitting translationaland rotational movement of the leaflets within the respective recesses.In preferred embodiments, each recess communicates with at least onegroove extending around an inner peripheral surface of the annular base,and a cleansing flow is directed vertically or angularly through therecess to the groove during antegrade circulation, and from the groovesthrough the recess during retrograde flow and valve closure. Thedirection of this cleansing flow through the recesses varies dependingupon the direction of circulation and the orientation of the leaflets,and is mostly unobstructed within the recesses by the leaflets. Theperipheral edges of the leaflets present minimal incursion or exposurebeneath the bottom of the annular base when the valve is completelyopen. When the leaflets of the valve are closed, the peripheral edge ofeach leaflet in the central region is preferably slightly spaced apartfrom the annular base to allow free movement of the leaflet and to avoidunsuccessful wear and/or stress. The peripheral edge of each leaflet inpreferred embodiments only contacts the annular base adjacent the grooveproximate the lateral regions of the leaflet.

In preferred embodiments, the angle at which fluid washing the surfacesof the annular base flows into the recesses is less than 35° to permitbetter washing dynamics. The preferred valve also has a dynamic pivotconstructed primarily on the lateral sides of the leaflets where twofulcrum edges are created by notches in the peripheral edge. Theleaflets pivot on each of the respective fulcrum edges at differentpoints in the opening and closing cycle of the valve. This swivel pivotmechanism also permits significant translational movement of theleaflets especially in the fully open position. This mechanism isbelieved to provide a pivot mechanism which permits the valve to openand close more rapidly than prior art bileaflet valves.

It is one object of this invention to design a bileaflet heart valveprosthesis of the type used for tricuspid or bicuspid (mitral) valvereplacement, and particularly one which provides superior operatingcapabilities and minimizes the risk to the patient when implanted usinga procedure involving preservation of the papillary muscle and chordalstructure by fixation to the posterior mitral annulus.

It is a related object of this invention to design the above bileafletvalve for implantation in either the anatomical or anti-anatomicalconfiguration, such that the peripheral edges of the leaflets present anextremely low incursion below the bottom surface of the annular base,and further present minimal radial and lateral exposure.

It is an additional object of this invention to design the abovebileaflet valve such that the passages through the bore of the valvebetween the leaflets provide substantially equal relative flow rates,thereby mitigating against flow differentials, gradients, or venturieffects which would otherwise cause turbulence or impede thetranslational or pivotal movement of the leaflets.

It is another object of this invention to design the present bileafletvalve such that it utilizes a “free floating leaflet” configuration withno pivot ears or projections, to thereby reduce and redistributemechanical or contact stresses otherwise focused on these pivot axis inconventional bileaflet valves.

It is a further object of this invention to design the above bileafletvalve such that it defines a cleansing channel or recess within theannular base in the region traversed by the lateral ends of theleaflets, and such that the cleansing channel is unobstructed withinthat region in a generally vertical direction, and induces or “steers”both vertical and angular fluid flow through that region duringantegrade and retrograde circulation.

It is another object of this invention to provide a bileaflet valve suchthat a shallow angle of less than about 35° may be formed between thelateral surfaces of the annular bore and the adjoining surfaces of therecesses which restrain the leaflets. It is believed that this willenhance cleansing of the recesses by normal antegrade and retrogradecirculation. Furthermore, because the recesses have unobstructed openchannels permitting easy antegrade and retrograde flow through therecesses, the surfaces within the respective recesses will permitenhanced washing action.

It is a further object of this invention to provide a bileaflet valvesuch that the peripheral edge of each leaflet is received within arecess and beneath a seat defined by the annular base, such that thereare no observable gaps between the annular base and peripheral edge inthe contact regions between the leaflets and annular base when viewedfrom a perspective along the longitudinal axis of the valve.

It is a fisher object of this invention to design the above bileafletvalve such that the annular base of the valve defines beveled arcuatesurfaces which contact the edges of the leaflets as the leaflets movebetween the open and closed positions, thereby creating a generallysmooth and continuous arcuate path along which the leaflets roll whenpivoting between the open and closed positions to distribute stressforces over an extended region of the leaflet and annular base.

The above-described features, advantages and objects, along with variousother advantages and features of novelty are pointed out withparticularity in the claims of the present invention annexed hereto andforming a part thereof. However, for a better understanding of theinvention, its advantages, and objects attained by its use, referenceshould be made to the drawings which form a further part hereof and tothe accompanying descriptive matter in which there is illustrated anddescribed preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing, in which like reference numerals indicate correspondingparts throughout the several views:

FIG. 1 is a perspective view of a preferred embodiment of the presentinvention showing the leaflets in a fully open position;

FIG. 2 is a lateral side view of the preferred bileaflet heart valve ofthe present invention shown in FIG. 1;

FIG. 3 is a lateral side view of the preferred bileaflet heart valveshown in FIG. 1;

FIG. 4 is a top plan view of the preferred bileaflet heart valve shownin FIG. 1;

FIG. 5 is a bottom plan view of the preferred bileaflet heart valveshown in FIG. 1;

FIG. 6 is a partially broken away elevated perspective view of theannular base of the preferred bileaflet heart valve shown in FIG. 1;

FIG. 7 is a cross-sectional side view of the lateral side of the annularbase of the preferred bileaflet heart valve shown in FIG. 1;

FIG. 8 is a cross-sectional side view of the traverse side of theannular base of the preferred bileaflet heart valve shown in FIG. 1;

FIG. 9A is an elevated perspective view of the bottom side of thepreferred leaflet shown in FIG. 1;

FIG. 9B is a cross-sectional perspective view of the preferred leafletshown in FIG. 1, in a manner similar to that shown in FIG. 9A, butproviding a perspective view only of a cross-section of the leaflet asseen from the line 9B-9B of FIG. 9A;

FIG. 10 is a bottom plan view of a leaflet of the preferred bileafletheart valve shown in FIG. 1;

FIG. 11 is a top plan view of a leaflet of the preferred bileaflet heartvalve shown in FIG. 1;

FIG. 12 is a vertical side view of a first lateral side of the leafletof the preferred bileaflet heart valve shown in FIG. 1;

FIG. 13 is a vertical side view of a second lateral side of the leafletof the preferred bileaflet heart valve shown in FIG. 1;

FIG. 14 is a horizontal side view of an upper edge, including the matingedge, of a leaflet of the preferred bileaflet heart valve shown in FIG.1;

FIG. 15 is a horizontal side view of the peripheral edge of the leafletof the preferred bileaflet heart valve shown in FIG. 1;

FIG. 16 is a diagrammatic cross-sectional view of the preferredbileaflet heart valve shown in FIG. 1 with the leaflets in a fully openposition;

FIG. 17 is a diagrammatic cross-sectional view of the preferredbileaflet heart valve shown in FIG. 1 illustrating the transition of theleaflets from a fully open position to a fully closed position;

FIG. 18 is a partially broken away cross-sectional view of the recess asseen from the line 18—18 of FIG. 7;

FIG. 19 is a partially broken away cross-sectional view of the recess asseen from the line 19—19 of FIG. 7;

FIG. 20 is a partially broken away cross-sectional view of the recesssimilar to that shown in FIG. 19 but generally showing a lateral sideportion of a leaflet within the recess when the leaflet is in a fullyclosed position as shown diagrammatically in FIG. 17;

FIG. 21 is a partially broken away cross-sectional view similar to FIG.20, but showing the leaflet in an open position as shown in FIG. 1;

FIG. 22 is an elevated perspective view of the preferred bileaflet heartvalve of the present invention similar to that shown in FIG. 1, exceptthat the leaflets are in a fully closed position;

FIG. 23 is a partially broken away bottom plan view of the preferredbileaflet heart valve shown in FIG. 22 when the leaflets are in a fullyclosed position;

FIG. 24 provides a graphic representation of the quantity of bloodflowing through a bileaflet heart valve during a single heartcontraction cycle wherein the positive quantity indicates blood flowingin an antegrade direction and the negative quantity below the “y” axisindicates the quantity of blood flowing in the retrograde direction;

FIG. 25 is a perspective view of a monoleaflet heart valve with anteriororientation as known to the prior art;

FIG. 26 is a perspective view of a bileaflet heart valve withanti-anatomical orientation;

FIG. 27 is a perspective view of a bileaflet heart valve with anatomicalorientation;

FIG. 28 is a perspective view of a monoleaflet heart valve withposterior orientation as known to the prior art; and

FIG. 29 is a perspective view of a bileaflet heart valve of the presentinvention implanted in an anatomical orientation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, a preferred bileaflet heart valveprosthesis 110 of the present invention and parts thereof areillustrated. The bileaflet heart valve prosthesis 110 of the presentinvention is preferably fabricated from a metal such a titanium, acarbon compound (or carbon with a minor percentage of silicon) such aspyrolytic carbon or the like, a metal alloy, or a suitable substratecoated with pyrolytic carbon as are well known in the art.

Referring now to FIGS. 25-29, a bileaflet heart valve 10 similar to thepreferred heart valve prosthesis 110 of the present invention is showndiagrammatically implanted within the heart 101 of a patient, with thevalve 10 sutured in place proximate to the mitral annulus 103 of theanatomical coronary valve and disposed above the papillary muscle andtendineae chordae 105 fixed to the posterior mitral annulus as describedpreviously. The bileaflet valve 10 may be implanted in either the fullyanatomical orientation or the fully anti-anatomical orientation as shownin FIGS. 26 and 27, respectively, or adjusted between the fullyanatomical and anti-anatomical orientations by rotating the valve 10within the corresponding suture ring (not shown) as is well known to theart. These orientations may be compared with the anterior and posteriororientations of a monoleaflet valve M shown in FIGS. 25 and 28.

Referring now to FIGS. 1-5, a preferred embodiment of the bileafletheart valve prosthesis 110 is described. The preferred bileaflet heartvalve 110 of the present invention shown in FIG. 1 includes an annularbase 112 and first and second leaflets 114. The fist and second leaflets114 are mounted within the annular base 112 for pivotal movement betweena fully open position, shown in FIGS. 1-5 and diagrammatically in FIG.16, and in phantom in FIG. 17, and in a fully closed position shown inFIGS. 22-23 and diagrammatically in FIG. 17. Referring now also to FIGS.68, the annular base 112 has a top surface 124 and an inner wall 126which defines a generally circular bore 116 passing through the annularbase 112 in a direction generally parallel with a longitudinal axis 128oriented generally in parallel with a vertical path for circulation offluid or blood through the generally circular bore 116.

The top surface 124 of the annular base 112 is raised proximate opposinglateral sides 129. On the inner wall 2 inner surface sidewall 126 of theannular base 112 proximate the opposing lateral sides 129, are flatportions 130 of lateral surfaces 133 which define flat lateral sides ofthe generally circular bore 116. The flat portions 130 of the lateralsurfaces 133 include a pair of recesses 132 in each of the respectivelateral sides 129 of the base 112. Further lateral depressions 135 arecentrally located in a lower portion of the inner surface 126 proximateeach of the two lateral sides 129, below and between the respectiverecesses 132 on each side, in the respective flat portions. In preferredembodiments, these depressions have a curvilinear surface which woulddefine a portion of one side of a cone. The recesses 132 extend into therespective flat portions 130 of the lateral surfaces 133, therebydisplacing a cylindrical bottom surface 140 of the recess 132 from therespective lateral surface 133 proximate the respective lateral side129. In preferred embodiments of the present invention, each of thecylindrical bottom surfaces 140 of the respective recesses 132 passthrough a cylindrical radius which is “feathered out” as the cylindricalsurface 140 approaches a junction with the respective lateral surface133.

Referring now also to FIGS. 18-21, a line 181, shown in FIG. 19, whichis tangential with a point on the cylindrical bottom surface 140 of therecess 132 just prior to a further point at which the cylindricalsurface 140 is “feathered out” to form a junction with the lateralsurface 133, lies at an angle “g′” to a tangent line 184 whichintersects line 181 and is tangential to the lateral surface 133. Inorder to properly measure the entrance angle “g′” to the recess 132, anumber of lines similar to line 181 which are tangential to a point onthe cylindrical surface 140 must be considered. This may be an infinitenumber of lines. The entrance angle, “g′”, will be the angle between thelines 184 and 181 which will be the greatest angle that exists betweenthe line 184 and any of the lines which can be drawn which intersectwith line 184 and are tangential to a point on the cylindrical surface140. This angle “g′”, is representative of a recess entrance angle tothe cylindrical recess 132. In preferred embodiments the recess entranceangle is less than about 35°. Preferably, the recess entrance angle “g′”is between about 20° and about 35°. More preferably, the recess entranceangle “g′” is from about 25° to about 34°. In even more preferredembodiments, the recess entrance angle “g′” ranges from about 28° toabout 33.5°. There is no preferred angle because the preferred angle mayvary in response to changes in other parameters, especially the diameterof the annular base 112. It will be appreciated that recesses to retainpivotal leaflets have existed in the bileaflet heart valve prostheses ofthe prior art for some time. It is believed, however, that a lowerrecess entrance angle will facilitate washing of the recess to minimizestagnation and potential for thrombogenic events in proximity to therecess 132. Therefore, it is believed that diminishing the angle ofentrance to the recess 132 will provide for better washing activity andlessen any potential for embolism which may exist in patients utilizingprosthetic heart valves.

Referring now also to FIGS. 9-15, the leaflets 114 have two sides, a topplanar surface 142 and a beveled bottom side 143. The bottom surface 143has a peripheral bevel portion 144 proximate the peripheral edge 150 anda central portion or central bevel 145 proximate a mating edge 148. Themating edge 148 has a narrow planar surface running nearly the entirewidth of the leaflet 114. The respective leaflets are mirror images ofone another in preferred embodiments so that when the respectiveleaflets 114 pivot to reside in the fully closed position, the matingedges 148 of the respective leaflets mate together to significantlyobstruct blood flow through the very limited space between therespective mating surfaces 148.

It will be appreciated that some blood will “regurgitate” between themating edges 148 of the respective leaflets 114 when they are closed.However, this is to be expected. In fact, such blood flow, while itshould be minimized, performs an important function of cleansing themating edges 148 as the blood regurgitates between the respective edges148.

The central beveled portion 145 of the beveled bottom side includes aflat planar surface 146 which is flanked on either side along the widthW of the leaflets 114, by curvilinear side surfaces 147 a and 147 bwhich rise up proximate lateral sides 151 of the leaflets 114 to flatside bevels 147 c and 147 d which separate the mating edges 148 from theperipheral bevel 144 on the beveled bottom side 143 proximate therespective lateral sides 151. The width Wps of the flat planar surface146 is greater than one-half of the width W of the leaflet 114, and istherefore a major portion of the central bevel 145. As used herein, thephrase “a major portion” means a portion of the whole which has a widthdimension which is at least as great as that of one-half of the width ofthe whole.

The respective lateral sides 151 of the respective leaflets 114 eachhave a cylindrical surface proximate the diamond-shaped cylindricalsurface 154. Notches 153, 155 are located adjacent to the diamond-shapedcylindrical surface 154. The inflow notches 153 are located generallybetween the diamond-shaped cylindrical surface 154 and the top edge ofthe leaflet 114. The generally V-shaped notch 153 is created and definedby an inflow flat 160 and an inflow side wall 156 of the diamond-shapedcylindrical surface 154. The generally V-shaped notch 155, called theoutflow notch 155, is created and defined by an outflow flat 162 and anoutflow side wall 158 of the diamond surface 154.

As previously discussed herein, washing of the various surfaces,crevices and the like by blood fluid passing through the heart valveprosthesis 110 is believed to be particularly important to reducestagnation and potentially thrombogenic activity. The present bileafletheart valve 110 is designed with this in mind. All of the surfaces ofthe present valve 110 are actively washed at one time or another in thepumping cycle of the heart in which the valve 110 is implanted. When thevalve 110 is in the fully opened position all of the surfaces of theside wall 126 are actively washed by blood flowing over the surfaces, asare the recesses 132. The leaflets 114 are also actively washed as theblood flows in the antegrade direction through the bore 116.

The diamond-shaped cylindrical surface 154 also has a cylindrical radiusgenerally consistent with the cylindrical radius of the bottom surface140 of the recess 132. As shown particularly in FIG. 22, when theleaflets 114 are in a fully closed position, some regurgitation of bloodthrough the bileaflet valve 110 occurs in the retrograde direction. Theregurgitation is desirable to a certain degree, so long as the energyefficiency of the pumping activity of the heart is not compromised. Theregurgitation occurs in a number of areas. Referring now also to FIG.22, and the other illustrations of the preferred bileaflet heart valve110, retrograde blood flow may pass between the mating surfaces 148 ofthe respective leaflets 114 as demonstrated by arrows 194, 195 and 196in FIG. 22. The bottom of the leaflets 114 also channel retrograde bloodflow into the recesses 132 by directing the blood against the seats 136created by the separation between the cylindrical bottom surface 140 andthe upper edge 134 of the recesses 132. An outflow side wall 158 of thediamond surface 154 may also channel retrograde blood flow to therecesses 132 and particularly to the seat 136. This flow will thenregurgitate between the leaflet 114 and the side wall 126 after it flowsover the seat 136 and come out proximate the regurgitationrepresentation arrows 191, 192 and 193. It will be appreciated that flowthrough areas where the top planar surface 142 meets the seat 136 willbe minimized and that this flow can be further minimized by widening theseat 136 further into the transverse side 131. Additional retrogradeblood flow will wash other portions of the valve 110, especiallyportions of the inner wall 126, including the lateral depressions 135and the flat portions of the lateral surfaces 133, and channel upwardsproximate arrow 192 in FIG. 22. It will be appreciated that there willalmost always be at least some separation between the peripheral edge150 of the leaflet 114 and the side wall 126. This enables retrogradeblood flow to regurgitate between the peripheral edge 150 and the sidewall 126 proximate the entire peripheral edge 150. Even where the topplanar surface 142 of the respective leaflets 114 are pressed againstthe respective seats 136, there is at least some space between theopposing surfaces for a very limited amount of “regurgitating”retrograde blood flow. The regurgitation is particularly significantproximate the transverse sides 131. This is particularly true because ofthe side wall surface 126 proximate the center of the peripheral edge150 is flush, thereby providing no obstruction to the retrograde flow ofblood. It will be appreciated that the seat 136 is fully diminished tonothing in this area in preferred embodiments. A further discussion ofthe seats 136 follows a further description of the leaflets 114immediately below.

Referring now particularly to FIGS. 16-21, a certain amount of “play”exists between the respective surfaces in the area of the diamondsurface 154 and the recess 132 when the leaflets 114 are in the openposition. This “play” permits a significant amount of translationalmovement. Because of the increased potential for translational movementbetween these surfaces when in the open position, the leaflets 114 havegreater freedom for translational motion than is either exhibited orgenerally possible in any of the prior art valves which have “matched”or “parallel” surfaces in both the open and closed positions. As showndiagrammatically in FIG. 17, when the leaflets 114 are in the fullyclosed position, the top planar surface 142 is pressed against the seat136 proximate the upper edge 134 of the recess 132. Althoughconsiderable separation appears to exist between these surfaces in FIG.17, this separation is exaggerated for clarity. During use of the valve110, the top planar surface 142 abuts against the seat 136. In actualfact, the spacial relationship between the top planar surface 142 andthe seat 136, when the leaflets 114 are in the closed position, is thatshown in FIG. 22, where the seat 136 cannot be separately called outbecause it is not visible in the view.

An axis 165, parallel with respective cylindrical surfaces ondiamond-shaped cylindrical surfaces 154 of the respective leaflets 114,and perpendicular the top surface 142 will lie at an angle “k” to anaxis 167, parallel with the respective cylindrical bottom surface 140 ofrespective recess 132, and perpendicular with the upper edge 134 of therecess 132, when the leaflets 114 are in the fully opened position. Whenthe leaflets 114 are in the fully closed position these respective axes165 and 167 will be either superimposed upon one another, or in parallelwith one another and the angle “k” will generally be about zero. In thisposition, therefore, the cylindrical surfaces 140 will be “matched” or“parallel” with the diamond-shaped surfaces 154 of the respectivelateral sides 151 of the respective leaflets 114. The angle “k”, showndiagrammatically in FIG. 17, is equal to the travel angle “k′”, when theleaflets 114 are in the fully open position.

It will be appreciated that significant translational movement ispermitted when the leaflets 114 are in the open position. This can beseen in FIG. 16 where the first axis 165 of the leaflet 114 lies at anangle “k” with respect to the second axis 167 of the cylindrical recessbottom surface 140. This translational movement of the leaflet 114, whenin the fully open position, is believed to allow the leaflet 114 to movefrom its fully open position to its fully closed position much fasterthan prior art devices. This is because the initial movement, when aretrograde flow of fluid begins, is an upward translational movement ofthe diamond-shaped surface 154 within the recess 132, until the top sidefulcrum edge 166 engages the upper edge sidewall or seat 136 within therecess 132. When the top side fulcrum edge 166 engages the seat 136within the recess 132, the leaflet 114 has already overcome any inertiait may have had when “resting” in the fully opened position. Thetranslational movement will subsequently give way to pivotal movement ofthe leaflet toward the fully closed position. This pivotal movement willoccur rapidly since the initial translational movement will provide somemomentum which will be translated into pivotal or annular movementtoward closure of the leaflets 114.

When the leaflet 114 is in the fully closed position, the initialmovement of the leaflet is more likely to be followed immediately by apivotal movement, because the cylindrical diamond-shaped surface 154 andthe cylindrical recess bottom surface 140 are more closely mated asshown in FIG. 20 and the separation allowing translational movement fromend to end is more limited. The leaflet 114 is likely to slip quicklyfrom the upper side edge 134 toward the lower side sidewall 138 of theleaflet 114. The leaflet will only begin to pivot after the bottom sidefulcrum edge 164 is engaged with the lower side sidewall 138. It will beappreciated, however, that the mechanism employed by the respectiveleaflets for pivoting is still a matter of inquiry and is not fullyunderstood at this time. It is believed, however, this dynamic pivotmechanism allows for faster opening and closing of the respective valves110. When the valve is in the open position, and the flow directionchanges from antegrade to retrograde, it is believed that the leaflet114 begins its linear motion immediately with the change in the flowdirection and the linear momentum is transferred into angular momentumas soon as the top side fulcrum edge or pivot 166 contacts the seat 136proximate the upper edge 134 of the recess 132. This is believed toresult in quicker closing than is exhibited by prior art devices.

It is believed that the preferred bileaflet heart valve prosthesis 110of the present invention provides for a lowered thrombus potential dueto the consideration given to access for washing in both the antegradeand retrograde directions. Furthermore, the dynamic pivot mechanism ofthe preferred leaflets 114 in cooperation with the preferred recesses132 are believed to provide for faster opening and closing of the valveand less friction in the pivot area due to the use of a “rolling” pivotmechanism wherein the pivot activity changes focus from the top sidefulcrum edge 166 to the bottom side fulcrum edge 164. The preferredvalve 110 also provides for a minimized travel angle “k′” between thefully opened position and the fully closed position. It is believed thatthe travel angle provided in the preferred valve 110 may represent atleast about 15-10° reduction in the travel angle as compared to many ofthe prior art devices. This reduction in the travel angle is believed tominimize angular velocity, wear, cavitation potential, and regurgitationvolume, while increasing overall efficiency.

The upper edges 134 for the preferred leaflets 114 are believed to slowthe leaflet 114 just before closure due to the presence of significantamounts of fluids which may be “squeezed” or compressed against thesidewall 126 of the annular base 112. Because the seats slow the leaflet114 just before closure, they are believed to have a minimizing effecton the cavitation potential. It is also believed that the use ofdiscontinuous seats, or seats which diminish prior to continuing into aseat extending from an opposite recess allows for a slight increase inregurgitation potential proximate the center portion of the leafletwhere cavitation potential is generally highest due to the likelihoodthat this area is likely to be subjected to a greater angular velocityas it comes toward closure against the sidewall 126. The seats 134 alsodecrease leakage or regurgitation proximate the lateral sides 129 of theannular base 112 when the leaflets 114 are in the closed position. Theseats 134 are also believed to provide for increased antegrade flow towash the flow channels or recesses 132 as the leaflets 114 close. As theleaflets 114 close the fluid in the recesses 132 begins to be “squeezed”or compressed within an upper portion of the recess distal to thetransverse sides 131 of the annular base 112. The width of the seats 134decreases as they extend from the recess 132 to the transverse side 131.Since there is no seat 134 in the center most region of the transverseside 131 in the preferred bileaflet heart valve 110, the fluid“squeezed” or compressed against the seats 134 is generally believed tobe released through the bore 116 after it washes at least a portion ofthe seat 134. While the leaflets 114 are in the closed position, theseats 134 serve to reduce retrograde leakage or regurgitation and atleast a portion of the retrograde flow is channeled around the diamondsurface 154, so as to thoroughly wash these areas when the leaflets 114are in a closed position.

The bottom surface of the recess 132 is in the form of a curvilinearcylindrical surface and is considered to have a generally cylindricalshape. As used herein, cylindrical surface or cylindrical shape means asurface formed by linear translation of a curve, or a surface which hasa radius similar to a portion of a surface of a cylinder. The diamondsurface 154 at the lateral sides 151 of the leaflets 114 have acylindrical shape which is “consistent” with or “mates” with thecylindrical recess bottom surfaces 140 of the recesses 132. However, asshown in FIG. 20, the diamond surface 154 is consistent with and mateswith the bottom surface 140 of the recess 132 only when the leaflet 114is in the closed position. However, when the leaflet is in the openposition, as shown in FIG. 21, and as previously discussed, significantroom for translational movement is provided. Furthermore, it will beappreciated that the bottom surface of the recess 140 and the matchedcylindrical diamond surface 154 of the leaflet 114 will not be inalignment when the leaflet is in any position other than a fully closedposition, thus allowing for significant clearance between the extremeedges of the diamond surfaces 154 and the extreme edges of the recesses132. Because of the increased potential for translational movement whenthe leaflets 114 are in positions other than the fully closed position,the leaflets 114 will exhibit greater translational freedom for motionthan is possible with prior art valves having parallel or matchedsurfaces in all positions as described and defined in descriptions ofthe prior art devices.

As shown particularly in FIG. 16, the flat planar surface 146 of thecentral bevel 145 and the peripheral bevel 144 of the bottom surface ofthe leaflet each lie generally in a plane respectively designated bytangent lines 172 and 174. As measured by the angle “a” between tangentlines 172 and 174, the peripheral bevel 144 and the flat planar surface146 of the central bevel 145 lie generally in planes which lie at anangle to one another. In preferred embodiments this angle will be lessthan 180°, or preferably at an angle of about 161° to about 178°, morepreferably about 166° to about 173°. In preferred embodiments, the angle“a” will be about 167° to about 172°. In the most preferred embodimentunder consideration, the angle “a” is about 169°. This bevel in thebottom surfaces of the leaflet 114, allows the angle of incidence for aflow of blood in the retrograde direction parallel with the longitudinalaxis 128 to be a greater angle of incidence in respect to the peripheralbevel 144 than with the flat planar surface 146 of the central bevel145. This is believed to be advantageous for at least two reasons.First, since there is a greater angle of incidence, the force of theblood flowing in the retrograde direction will have greater impact uponthe leaflet 114 and cause it to pivot toward the fully closed positionmore rapidly than might otherwise be expected. Furthermore, thedifference between the respective bevels, and the angle of the tangentline 176 to the top planar surface 142 allow the peripheral edge 150 tohave a shorter radial closing distance to travel before the leaflet 114is in the fully closed position than might be expected for a leaflethaving parallel surfaces.

In preferred embodiments, the angle of the plane in which the flatplanar surface 146 of the central bevel 145 rests, to a horizontal plane170, which angle is consistent with the angle between tangent line 172and the plane 170, will be an angle “a′”. In preferred embodiments, “a′”may range from about 84° to about 97°, preferably about 86° to about95°, more preferably about 88° to about 94°, more preferably about 90°to about 92°, more preferably more than 90°, and in the most preferredembodiments, “a′” will be either 91°, or 91° or more. Similarly, theangle between the plane in which the peripheral bevel 144 rests, and thehorizontal plane 170 may be measured by taking the angle “b′” betweenthe tangent line 174 and the horizontal plane 170. In preferredembodiments, the angle “b′” will be less than 87°, preferably less than86°. In preferred embodiments, “b′” will range from about 78° to about84°, preferably about 80° to about 82°, and most preferably, it will beabout 81°. Similarly, the angle of the plane in which the top planarsurface 142 of the top side of the leaflet 114 rests, will lie at anangle “c′” to the horizontal plane 170 as measured between the tangentline 176 and the horizontal plane 170 when the leaflet is in the fullyopen position. In preferred embodiments, “c′” is greater than about 78°and less than 90°, and preferably in a range of from about 82° to about89°, preferably about 84° to about 88°. In the most preferredembodiment, “c′” is about 86°.

As shown particularly in phantom in FIG. 17, when the leaflet 114 beginsto pivot from the fully open position to the fully closed position inresponse to force exerted upon the peripheral bevel 144, the force isbelieved to result in an initial translational movement of the leafletto lift leaflet 114 within the recess 132. When the leaflet 114 hasreached the fully closed position shown diagrammatically in FIG. 17, anarea on the top planar surface 142 proximate the peripheral edge 150generally proximate the respective lateral sides 151 will abut againstthe seat 136 on either lateral side 129 and extending at least partiallyinto the adjacent transverse side 131. When the leaflet 114 is in thefully closed position, the respective mating edges 148 will generallyrest against one another while generally allowing at least someretrograde regurgitation of blood between the respective mating surfaces148.

It will be appreciated that the preferred embodiment of the bileafletheart valve prosthesis 110 of the present invention will not have anysharp edges and that all edges will in fact be polished, smoothed orfeathered so as to minimize shearing of blood as it passes over any ofthese edges. These smooth “transitions” between surfaces of all kindswill be obtained by shaving and polishing all edges so that the edgesare rounded and have a smooth transition from one plane to another. Anyradial surfaces of course will be polished as well.

As shown in FIG. 22, the amount of regurgitation of blood in theretrograde direction is believed to be significant enough to provideappropriate cleansing of the valve 110. Heart valves are generallydesigned with at least some regurgitation in mind so long as theregurgitation does not reduce the efficiency of the heart. It isbelieved that the regurgitation is important to permit the washing ofthe various surfaces of the present prosthetic device. FIG. 24 generallyprovides a representation of the quantity (Q) of blood flowing through abileaflet heart valve during a contraction cycle when the valve is inthe aortic position. During systole, the quantity of blood passingthrough the valve in the antegrade direction (+) is fairly significant.As the force from the contraction diminishes from its highest point,indicated at the apex of the curve (Qsys), until the antegrade flow endsand blood begins to flow in the retrograde direction (−), the leaflets114 remain in an open position. The retrograde flow then begins to pushthe leaflets 114 toward the closed position at the lowest point of thecurve below the “y” axis (Qcl). As the leaflets 114 close, most of theretrograde flow is obstructed, but not all of it. The remainingretrograde flow is due to leakage around the leaflets 114. Theretrograde leakage (Ql) has been discussed herein and is believed tohave a positive effect in respect to washing the various surfaces of theprosthetic heart valve, in that this “regurgitation” will “wash” thesurfaces to reduce stagnation of blood as a measure against potentialthrombus.

As shown particularly in FIGS. 6 and 7 and demonstrated diagrammaticallyin FIG. 23, the upper edge 134 blends or “feathers” into the inner wall126 of the annular base 112, as does the seat 136, in preferredembodiments. It is believed that this has a very positive effect uponpreservation of the integrity of the top planar surface 142 of therespective leaflets 114 by reducing cavitation potential. This isparticularly true in an area approximately 15° to either side of acenter line 184 bisecting a leaflet 114, and in the areas most proximateto the peripheral edge 150. The potential for negative effects ofcavitation upon the top planar surface 142 is also reduced by theshortened travel angle “k′” between the location of the top planarsurface 142 when the leaflet is in the fully open position, and the topplanar surface 142 when the leaflet is in the fully closed position asrepresented by tangent line 179 of FIG. 17. Because the preferredleaflet 114 of the present invention has a “double-beveled” bottomsurface, the position of the top planar surface 142 in relation to theside wall 126 can be minimized to reduce the radial distance “k′”traveled by the top planar surface 142 in moving to the closed position.In this way, the angular speed of the movement of the most distalportion of the top planar surface 142 proximate the peripheral edge 150,where the cavitation potential is generally believed to be the greatest,is diminished gradually when the leaflet 114 approaches the closedposition. Cavitation potential is also minimized because the distance isminimized by the beveled design of the leaflets 114. In this regard, itwill be appreciated that the leaflet will continue to gain speed as itpivots through a greater radial distance. Therefore, by minimizing theradial distance between the open position and the closed position, theradial speed of the leaflet 114 can be minimized. In preferredembodiments, the travel angle “k′” will be from about 37° to about 58°,preferably about 39° to about 56°, even more preferably about 40° toabout 55°, and most preferably about 45° to about 50°. Cavitationpotential is also reduced because the seats 136, extending from therespective recesses 132 on the respective lateral sides of the leaflet114, help to slow the closure or “cushion” the closure of the leafletagainst the side wall 126 because the blood between the peripheral edge150 and the proximate portions of the top planar surface 142 must be“squeezed” out of the intervening space adjacent the respective seat 136as the leaflet 114 is pivoting toward the fully closed position.Furthermore, a gap 171 (shown in FIG. 8) between the seats 136 of theopposing lateral sides extending into the transverse side permits acontinuing flow of blood in the retrograde direction which also helps toprevent the formation of a vacuum on the top planar surface 142proximate the peripheral edge 150 which is generally the genesis ofcavitation damage on the planar surfaces of a leaflet 114. The“cushioning” effect of the partial or “discontinuous” seats 136 alsohelps to prevent stress to other portions of the leaflet 114 as theycollide with the side wall 126 or the seat 136.

In FIG. 23, a center line 184 extending from a center point 182 is shownsuperimposed upon a bottom surface of a leaflet 114. In preferredembodiments, the respective seats 136 extending from respective recesses132 will extend only as far as the radius lines 185 and 186 which areradially equidistance from the center line 184. For this reason, theradial angle “i′” will equal the radial angle “h′” between the radiuslines 186, 185 and the center line 184, respectively, and the radialangle “j′” will equal twice either of the equal angles “i′” and “h′”. Inpreferred embodiments, the radial angle of “j′” will range from about 5°to about 55°, preferably about 10° to about 50°, more preferably about15° to about 45°, even more preferably about 20° to about 40°, even morepreferably about 25° to about 35°, and even more preferably about 30°.The reason for limiting the extension of the seats 136 entirely throughthe inner wall 126 proximate the transverse surface 131 is in partbecause of a desire to minimize the cavitation potential which isgenerally greatest within 15° on either side of a center line 184bisecting the top planar surface 142 of a pivotal leaflet 114 of abileaflet heart valve. It will be understood that the area having thegreatest cavitation potential is likely to be at the most distal portionof the top planar surface 142 from the center point 182, because it isthis portion of the leaflet 114 which gains the most angular speed whenthe leaflet is pivoting toward closure and is most capable of generatingthe force required to create cavitation bubbles on the top planarsurface 142. Therefore, eliminating the seat 136 in this particulararea, is expected to minimize cavitation potential by permitting moreregurgitation through the gap 171.

While the preferred embodiments of the above bileaflet heart valve 10,110 have been described in detail with reference to the attacheddrawings, it will be understood that various changes and adaptations maybe made in the bileaflet heart valve 10, 110 without departing from thespirit and scope of the appended claims. It is to be understood thateven though numerous characteristics and advantages of variousembodiments of the present invention have been set forth in theforegoing description, together with details of the structure andfunction of various embodiments of the invention, this disclosure isillustrative only and changes may be made in detail, especially inmatters of shape, size and arrangement of parts, within the principlesof the present invention, to the full extent indicated by the broadgeneral meaning of the terms in which the appended claims are expressed.

What is claimed is:
 1. A bileaflet heart valve prosthesis for controlling a circulation of a fluid within a heart of a patient, said bileaflet heart valve prosthesis comprising: an annular base and first and second leaflets, the first leaflet and the second leaflet being mounted within the annular base for pivotal movement between a fully closed position and a fully open position, the annular base defining a vertical bore extending through the base; each of the respective leaflets having first and second sides, the first side being a top side and the second side being a bottom side, the bottom sides of the respective leaflets generally facing one another when the respective leaflets are in an open position; each bottom side having an upper half and a lower half, a major portion of the upper half providing an upper surface lying generally in a first plane and a lower half providing a lower surface lying generally in a second plane, the first plane lying at an angle to the second plane; a third plane passing through a horizontal cross-section of the annular base, the first and second planes lying at angles to the third plane when the leaflets are in either the open or closed positions; wherein the first plane of each of the respective leaflets extends beyond an angle of 90 with respect to the third plane when the leaflets go from the fully closed position to the fully open position, the annular base having a first lateral side having a first lateral surface, a second lateral side having a second lateral surface, and a pair of transverse sides individually disposed between the first and second lateral sides, the annular base defining a first recess extending radially outward into the annular base from and communicating with the bore, and a second recess extending radially outward into the annular base from and communicating with the bore, the first recess being disposed within the first lateral side, the second recess being disposed within the second lateral side, wherein at least a first side portion of the first leaflet is received within the first recess and at least a second side portion of the first leaflet is received within said second recess to retain the first leaflet within the annular base, wherein the annular base further defines third and fourth recesses extending radially outward into the annular base from and communicating with the bore, the third recess being disposed within the first lateral side and the fourth recess being disposed within the second lateral side, wherein at least a third side portion of the second leaflet is received within the third recess and at least a fourth side portion of the second leaflet is received with the fourth recess to retain the second leaflet within the annular base; the first, second, third and fourth side portions of the respective leaflets each having a plurality of recess engagement surfaces, two of the plurality of recess engagement surfaces meeting to form a first fulcrum edge and two of the plurality of recess engagement surfaces meeting to form a second fulcrum edge removed from the first fulcrum edge, each of the recesses having an upper and lower recess side surface, wherein each of the respective first and second fulcrum edges engage an upper or lower recess side surface of the recess in which the respective side portion is engaged when the respective leaflet pivots either from the fully open position to the fully closed position or from the fully closed position to the fully open position such that engagement between one of the respective fulcrum edges and the respective side surface of each of the respective recesses is changeable from engagement with a side surface by the first fulcrum edge to engagement with a side surface by the second fulcrum edge as the respective leaflet pivots from one position to the other.
 2. The bileaflet heart valve prosthesis of claim 1, wherein the first and second planes lie at first and second angles respectively to the third plane passing through the horizontal cross-section of the annular base when the respective leaflets are in the fully open position, the first angle being greater than 90° and the second angle less than 87°.
 3. The bileaflet heart valve prosthesis of claim 2, wherein the angle between the first plane and the second plane is from about 161° to about 178°.
 4. The bileaflet heart valve prosthesis of claim 1, wherein the respective top sides have top surfaces which lie generally in respective top planes and each of the top planes changes position from a first position to a second position when the respective leaflet changes position from the fully open position to the fully closed position, wherein a travel angle is an angle between the respective top plane when the leaflet is in the first position and the respective top plane when the leaflet is in the second position, and wherein the travel angle for each of the first and second leaflets is from about 40° to about 55°.
 5. The bileaflet heart valve prosthesis of claim 4, wherein a horizontal plane, which is perpendicular to the lateral sides of the annular base, passes through a horizontal cross-section of the base, and each of the respective top planes lie at a greater angle to the horizontal plane than the second plane on the respective lower surface.
 6. The bileaflet heart valve prosthesis of claim 1, wherein each of the respective leaflets having first and second sides, the first side being a top side and the second side being a bottom side, the bottom sides of the respective leaflets generally facing one another when the respective leaflets are in an open position; each bottom side having an upper surface lying generally in a first plane and a lower surface lying generally in a second plane, the first plane lying at an angle to the second plane.
 7. A bileaflet heart valve prosthesis for controlling a circulation of a fluid within a heart of a patient, said bileaflet heart valve prosthesis comprising: an annular base and first and second leaflets, the first leaflet and the second leaflet being mounted within the annular base for pivotal movement between a fully closed position and a fully open position, the annular base defining a vertical bore extending through the base; each of the respective leaflets having first and second sides, the first side being a top side and the second side being a bottom side, the bottom sides of the respective leaflets generally facing one another when the respective leaflets are in an open position; each bottom side having an upper half and a lower half, a major portion of the upper half providing an upper surface lying generally in a first plane and a lower half providing a lower surface lying generally in a second plane, the first plane lying at an angle to the second plane; a third plane passing through a horizontal cross-section of the annular base, the first and second planes lying at angles to the third plane when the leaflets are in either the open or closed positions; wherein the first plane of each of the respective leaflets extends beyond an angle of 90 with respect to the third plane when the leaflets go from the fully closed position to the fully open position, the annular base defining a bore extending through the base, the base having a longitudinal axis oriented generally in parallel with the bore and the circulation of the fluid through the bore, the annular base having a first lateral side having a first lateral surface, a second lateral side having a second lateral surface, and a pair of transverse sides individually disposed between the first and second lateral sides, the annular base defining a first recess extending radially outward into the annular base from and communicating with the bore, and a second recess extending radially outward into the annular base from and communicating with the bore, the first recess being disposed within the first lateral side, the second recess being disposed within the second lateral side, the first recess having a first recess bottom surface, the first recess bottom surface intersecting the first lateral surface of the base such that the first recess bottom surface and the first lateral surface form a first junction, a first recess entrance angle being the largest of a plurality of angles between a first line generally tangential with the first lateral surface proximate the first junction and any of an infinite number of second lines intersecting the first line and generally tangential with any portion of the first recess bottom surface proximate the first junction, the second recess having a second recess bottom surface intersecting the second lateral surface such that the second recess bottom surface and the second lateral surface form a second junction, a second recess entrance angle being the largest of a plurality of angles between a third line tangential with the second lateral surface proximate the second junction and any of an infinite number of fourth lines intersecting the third line and tangential with any portion of the second recess bottom surface proximate the second junction; wherein at least a first side portion of the first leaflet is received within the first recess and at least a portion of the first leaflet is received within said second recess to retain the first leaflet within the annular base; the improvement characterized in that each of the first and second recess entrance angles are less than about
 35. 8. The bileaflet heart valve prosthesis of claim 7 wherein the first and second recess entrance angles range from about 18° and about 34°.
 9. The bileaflet heart valve prosthesis of claim 7 wherein the first and second recess bottom surfaces are cylindrical surfaces.
 10. The bileaflet heart valve prosthesis of claim 7 wherein the annular base further define third and fourth recesses extending radially outward into the annular base from and communicating with the bore, the third recess being disposed within the first lateral side and the fourth recess being disposed within the second lateral side, the third recess having a third recess bottom surface intersecting the first lateral surface such that the third recess bottom surface and the first lateral surface form a third junction, a third recess entrance angle being the largest of a plurality of angles between a fifth line generally tangential with the first lateral surface proximate the third junction and any of an infinite number of sixth lines intersecting the fifth line and generally tangential with any portion of said third recess bottom surface proximate the third junction, the fourth recess having a fourth recess bottom surface intersecting the second lateral surface, the fourth recess bottom surface and the second lateral surface intersecting to form a fourth junction, a fourth recess entrance angle being the largest of a plurality of angles between a seventh line generally tangential with the second lateral surface proximate the fourth junction and any of an infinite number of eighth lines intersecting the seventh line and generally tangential with any portion of the fourth recess bottom surface proximate the fourth junction, each of the third and fourth recess entrance angles being less than about 35°, wherein at least a third side portion of the second leaflet is received within the third recess and at least a fourth side portion of the second leaflet is received with the fourth recess to retain the second leaflet within the annular base.
 11. The bileaflet heart valve prosthesis of claim 9, the first bileaflet having a peripheral edge, wherein the respective side portions of the first leaflet which are received within the first and second recesses each have a cylindrical surface along the peripheral edge proximate the respective side portions received within the respective recesses.
 12. The bileaflet heart valve prosthesis of claim 11, the first leaflet having a complimentary pair of notches in the peripheral edge proximate each of the respective side portions of the first leaflet which are received within the respective first and second recesses, wherein the complimentary pair of notches cooperate to permit the leaflet to pivot within the respective recess.
 13. The bileaflet heart valve prosthesis of claim 9, wherein each of the respective side portions of the respective leaflets have a cylindrical side surface along a peripheral edge of the leaflet proximate the respective side portion which is received within the respective recess, wherein the respective cylindrical side surfaces mate with the respective cylindrical bottom surfaces of the respective recess in which the respective side portions are received when the respective leaflets are in the closed position.
 14. The bileaflet heart valve prosthesis of claim 9, the first bileaflet having a peripheral edge, wherein the respective side portions of the first leaflet, which are received within the first and second recesses, each have a cylindrical surface along the peripheral edge proximate the respective side portions received within the respective recesses.
 15. The bileaflet heart valve prosthesis of claim 14, the first leaflet having a complimentary pair of notches in the peripheral edge proximate each of the respective side portions of the first leaflet which are received within the respective first and second recesses, wherein the complimentary pair of notches cooperate to permit the leaflet to pivot within the respective recess and the cylindrical surfaces of the respective peripheral edges mate with the cylindrical bottom surfaces of the respective recesses in which the respective recesses in which the respective side portions are received when the first leaflet is in the closed position.
 16. A bileaflet heart valve prosthesis for controlling a circulation of a fluid within a heart of a patient, said bileaflet heart valve prosthesis comprising: an annular base and first and second leaflets, the first leaflet and the second leaflet being mounted within the annular base for pivotal movement between a fully closed position and a fully open position, the annular base defining a vertical bore extending through the base; each of the respective leaflets having first and second sides, the first side being a top side and the second side being a bottom side, the bottom sides of the respective leaflets generally facing one another when the respective leaflets are in an open position; each bottom side having an upper half and a lower half, a major portion of the upper half providing an upper surface lying generally in a first plane and a lower half providing a lower surface lying generally in a second plane, the first plane lying at an angle to the second plane; a third plane passing through a horizontal cross-section of the annular base, the first and second planes lying at angles to the third plane when the leaflets are in either the open or closed positions; wherein the first plane of each of the respective leaflets extends beyond an angle of 90 with respect to the third plane when the leaflets go from the fully closed position to the fully open position, the annular base having a first lateral side having a first lateral surface, a second lateral side having a second lateral surface, and a pair of transverse sides individually disposed between the first and second lateral sides, the annular base defining a first recess extending radially outward into the annular base from and communicating with the bore, and a second recess extending radially outward into the annular base from and communicating with the bore, the first recess being disposed within the first lateral side, the second recess being disposed within the second lateral side, wherein at least a portion of the first leaflet is received within the first recess and at least a portion of the first leaflet is received within said second recess to retain the first leaflet within the annular base, wherein the annular base further defines third and fourth recesses extending radially outward into the annular base from and communicating with the bore, the third recess being disposed within the first lateral side and the fourth recess being disposed within the second lateral side, wherein at least a portion of the second leaflet is received within the third recess and at least a portion of the second leaflet is received with the fourth recess to retain the second leaflet within the annular base; wherein each leaflet has an upper surface and a curved peripheral edge and each recess has an upper side and a lower side, the upper side extending from the respective recess proximate the respective lateral side to a location on an adjacent transverse side, the upper edge of each recess forming a seat against which an area on the upper surface, proximate the curved peripheral edge, of a leaflet engaged within the respective recess, can abut when the leaflet is in the closed position, the improvement characterized in that each of the respective upper edges forms a seat which extends from one recess toward another and diminishes to become a smooth surface which is flush with the respective lateral surface.
 17. The bileaflet heart valve prosthesis of claim 13, wherein each upper side has an end point where the seat diminishes into the respective lateral surface and no longer provides a seat against which the upper surface proximate the peripheral edge can abut, wherein the annular base has an inner wall which includes the lateral surface and the annular base has a radial distance which extends 360° around the inner wall, wherein the upper side extending from the first recess is the first upper side and the upper side extending from the second recess is the second upper side and the radial distance between the respective end points of the first and second upper sides is from about 5° to about 55°. 